Typically in communication systems such as CDMA and, more particularly, CDMA evolutions such as WCDMA, dedicated channels are required for sending data and also for control of the system. Within the forward link of such systems, a single channel is used to carry the information to be transmitted and characteristics of the transmitted information are conveyed on another separate forward control channel. Each of these channels occupies a Walsh code from a finite set of available Walsh codes. To keep the system from becoming Walsh code limited it is important to conserve Walsh code resources. The allocation of these dedicated channels for each user typically requires rapid shuffling between dormant and active states to free up Walsh code resources.
In order to afford more efficient allocation of bits and Walsh codes resources in a spread spectrum communication system, a U.S. patent application Ser. No. 09/703,775 that was filed on Nov. 1, 2000 and entitled “Apparatus and Method for Providing Separate Forward Dedicated and Shared Control Channels in a Communications System,” proposed utilizing a Dedicated Pointer Control Channel (DPTRCH), a Shared Control Channel (SHCCH), and a Shared Channel (SHCH), for communications between a transmitting communication device and a receiving communication device. The SHCH may be dynamically allocated among multiple communication devices in a communication system based on information in each of the DPTRCH and the SHCCH.
When a communication system includes a SHCH that is dynamically allocated among multiple receiving communication devices, it is possible for a communication device to decode the wrong SHCH data, that is, SHCH data that is intended for a different communication device. For example, a communication device may listen to a DPTRCH that was previously dedicated to the communication device but is now dedicated to a different communication device, with the result that the communication device decodes SHCCH data intended for the other communication device and may result in the communication device decoding SHCH data intended for the other communication device. Or a communication device may erroneously decode the data in a DPTRCH intended for it and be pointed to the wrong SHCCH.
Decoding data that is intended for a different communication device can create throughput problems in automatic repeat request (ARQ) and Hybrid ARQ (HARQ) communication systems. In an ARQ communication system, correct delivery of data is assured by a receiving communication device requesting retransmissions of erroneously received blocks of data. A HARQ system is similar to an ARQ system in that a receiving communication device requests retransmissions of all data blocks that have been received in error. However, HARQ also saves and uses failed data blocks, that is, the data blocks that have been received in error, at the receiving communication device to increase the coding gain. The failed data blocks are combined with, and jointly decoded with, a currently received data block in order to improve performance.
When a failed data block is not an incorrectly received version of a retransmitted data block, but is instead a data block that was intended for a different communication device, the stored, failed data block can corrupt all previously received data with which it is combined and jointly decoded. For example, a communication device may be in the midst of reception of a data packet comprising multiple transmitted frames when the communication device erroneously decodes a DPTRCH frame and in turn decodes the wrong SHCH. Correct decoding then becomes very difficult, possibly resulting in multiple retransmissions of data by the transmitting communication device up to a predetermined maximum number of retransmissions. The repeated retransmissions of data when there is little chance that the data is going to be correctly decoded is wasted throughput.
Therefore a need exists for preventing improperly decoded data blocks from corrupting previously processed data blocks.